Systems and methods of providing server initiated connections on a virtual private network

ABSTRACT

The present invention is related to a method for establishing via an appliance a transport layer protocol connection initiated by a server on a first network to a client connected from a second network to the first network via a secure socket layer virtual private network (SSL VPN) connection. The method includes the step of receiving, by an appliance, a transport layer connection request from a server on a first network to connect to a client connected to the first network via a SSL VPN connection from a second network. The transport layer connection request identifies a client destination internet protocol address and a client destination port on the first network. The method includes establishing, by the appliance, a first transport layer connection to the server on the first network, determining, by the appliance, the client on the second network associated with the client destination internet protocol address on the first network, and transmitting, by the appliance, connection information identifying the client destination port to an agent on the client. The agent establishes a second transport layer connection to the client destination port using a local internet protocol address of the client on the second network and establishes a third transport layer connection to the appliance, which it associates with the second transport layer connection.

RELATED APPLICATION

This present application claims priority to and is a continuation ofU.S. patent application Ser. No. 11/465,950, entitled “SYSTEMS ANDMETHODS OF PROVIDING SERVER INITIATED CONNECTIONS ON A VIRTUAL PRIVATENETWORK”, filed Aug. 21, 2006, which is incorporated herein by referencein its entirety.

FIELD OF THE DISCLOSURE

The present invention generally relates to data communication networksand, in particular, to systems and methods for providing serverinitiated connections to a client connected via a secure socket layervirtual private network connection.

BACKGROUND

In conventional systems, virtual private networks (VPN) provide a clientcomputer with secure access to a private network. Typically, the clientis assigned an internet protocol (IP) address on the private networkafter a VPN server authenticates the client. Once the client isauthenticated and can access the VPN, the client may securely accessresources residing on the private network. In many cases, VPNs provide aremote client on a public network access to server on a private network,such as a corporate network. In some cases, the VPN connected clientalso has resources that would be useful to access by a computing deviceon the private network, such as a server. For example, the VPN connectedclient may have files to be transferred to the private network. However,a virtual private network system may not enable a computing device onthe private network to initiate and establish a connection to a virtualprivate network connected client.

It would, therefore, be desirable to provide systems and methods forefficiently allowing a server in a private network to initiate aconnection to a remote client connected to the private network via avirtual private network connection.

BRIEF SUMMARY

The present solution of the appliance and client agent described hereinprovides techniques for allowing efficient and transparent serverinitiated connections over a virtual private network connection to aclient. As such, servers and SSL VPN clients can transparentlycommunicate via connections established by either the server or theclient. The SSL VPN clients seamlessly appear as clients on the networkaccessed or managed by the appliance. This enables SSL VPN users to takeadvantage of applications, such as collaboration tools, that use serverinitiated connections. Additionally, clients of SSL VPN users canprovide access to applications and collaboration tools to the otherclients and servers on the private network accessed via the virtualprivate network connection.

In one aspect, the present invention is related to a method forestablishing via an appliance a transport layer protocol connectioninitiated by a server on a first network to a client connected from asecond network to the first network via a secure socket layer virtualprivate network (SSL VPN) connection. The method includes the step ofreceiving, by an appliance, a transport layer connection request from aserver on a first network to connect to a client connected to the firstnetwork via a SSL VPN connection from a second network. The transportlayer connection request identifies a client destination internetprotocol address and a client destination port on the first network. Themethod includes establishing, by the appliance, a first transport layerconnection to the server on the first network, determining, by theappliance, the client on the second network associated with the clientdestination internet protocol address on the first network, andtransmitting, by the appliance, connection information identifying theclient destination port to an agent on the client. The agent establishesa second transport layer connection to the client destination port usinga local internet protocol address of the client on the second networkand establishes a third transport layer connection to the appliance. Theagent associates the third transport layer connection with the secondtransport layer connection. In one embodiment, the agent comprises a webbrowser plug-in.

In some embodiments, the method includes linking, by the appliance, thefirst transport layer connection to the server with the third transportlayer connection to the agent of the client. In another embodiment, themethod includes generating, by the appliance, a first connection recordfor the first transport layer connection to the server, receiving, bythe appliance, a second connection record from the agent for the thirdtransport layer connection, and associating, by the appliance, the firstconnection record with the second connection record. In one embodiment,the method includes transmitting, by the appliance, to the agent via acontrol channel connection established between the appliance and theagent. In some embodiments, the connection information transmitted fromthe appliance to the agent includes a protocol, a server internetprotocol address, or a server source port.

In another embodiment, the method includes the appliance forwarding,data received from a server internet protocol address and server sourceport to an internet protocol address and port used by the agent for thethird transport layer connection. In some of these embodiments, theagent provides the data to the application via the second transportlayer connection.

In one embodiment, the method includes transmitting, by the client, viathe appliance a request to the server to transmit the transport layerconnection request. In another embodiment, the appliance determines viacontent of an application layer protocol used for communications betweenthe client and the server a server destination internet protocol addressand server port or the client destination internet protocol address andclient destination port. In some embodiments, the appliance modifies thecontent of the application layer protocol transmitted to the server toidentify an internet protocol address of the client on the firstnetwork.

In yet another embodiment, the method includes determining, by theappliance, a second server initiated transport layer connection requestto the client exceeds a predetermined threshold identifying a number ofserver initiated transport layer connections allowed to the client, andnot establishing, by the appliance, the second server initiatedtransport layer connection.

The details of various embodiments of the invention are set forth in theaccompanying drawings and the description below.

BRIEF DESCRIPTION OF THE FIGURES

The foregoing and other objects, aspects, features, and advantages ofthe invention will become more apparent and better understood byreferring to the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1A is a block diagram of an embodiment of a network environment fora client to access a server via an appliance;

FIG. 1B is a block diagram of an embodiment of an environment fordelivering a computing environment from a server to a client via anappliance;

FIGS. 1C and 1D are block diagrams of embodiments of a computing device;

FIG. 2A is a block diagram of an embodiment of an appliance forprocessing communications between a client and a server;

FIG. 2B is a block diagram of another embodiment of an appliance foroptimizing, accelerating, load-balancing and routing communicationsbetween a client and a server;

FIG. 3 is a block diagram of an embodiment of a client for communicatingwith a server via the appliance;

FIG. 4A is a block diagram of an embodiment of an appliance providing aserver initiated connection to a virtual private network connectedclient; and

FIG. 4B is a flow diagram depicting steps of an embodiment of a methodfor practicing a technique for providing a server initiated connectionto a virtual private network connected client.

The features and advantages of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements.

DETAILED DESCRIPTION A. Network and Computing Environment

Prior to discussing the specifics of embodiments of the systems andmethods of an appliance and/or client, it may be helpful to discuss thenetwork and computing environments in which such embodiments may bedeployed. Referring now to FIG. 1A, an embodiment of a networkenvironment is depicted. In brief overview, the network environmentcomprises one or more clients 102 a-102 n (also generally referred to aslocal machine(s) 102, or client(s) 102) in communication with one ormore servers 106 a-106 n (also generally referred to as server(s) 106,or remote machine(s) 106) via one or more networks 104, 104′ (generallyreferred to as network 104). In some embodiments, a client 102communicates with a server 106 via an appliance 200.

Although FIG. 1A shows a network 104 and a network 104′ between theclients 102 and the servers 106, the clients 102 and the servers 106 maybe on the same network 104. The networks 104 and 104′ can be the sametype of network or different types of networks. The network 104 and/orthe network 104′ can be a local-area network (LAN), such as a companyIntranet, a metropolitan area network (MAN), or a wide area network(WAN), such as the Internet or the World Wide Web. In one embodiment,network 104′ may be a private network and network 104 may be a publicnetwork. In some embodiments, network 104 may be a private network andnetwork 104′ a public network. In another embodiment, networks 104 and104′ may both be private networks. In some embodiments, clients 102 maybe located at a branch office of a corporate enterprise communicatingvia a WAN connection over the network 104 to the servers 106 located ata corporate data center.

The network 104 and/or 104′ be any type and/or form of network and mayinclude any of the following: a point to point network, a broadcastnetwork, a wide area network, a local area network, a telecommunicationsnetwork, a data communication network, a computer network, an ATM(Asynchronous Transfer Mode) network, a SONET (Synchronous OpticalNetwork) network, a SDH (Synchronous Digital Hierarchy) network, awireless network and a wireline network. In some embodiments, thenetwork 104 may comprise a wireless link, such as an infrared channel orsatellite band. The topology of the network 104 and/or 104′ may be abus, star, or ring network topology. The network 104 and/or 104′ andnetwork topology may be of any such network or network topology as knownto those ordinarily skilled in the art capable of supporting theoperations described herein.

As shown in FIG. 1A, the appliance 200, which also may be referred to asan interface unit 200 or gateway 200, is shown between the networks 104and 104′. In some embodiments, the appliance 200 may be located onnetwork 104. For example, a branch office of a corporate enterprise maydeploy an appliance 200 at the branch office. In other embodiments, theappliance 200 may be located on network 104′. For example, an appliance200 may be located at a corporate data center. In yet anotherembodiment, a plurality of appliances 200 may be deployed on network104. In some embodiments, a plurality of appliances 200 may be deployedon network 104′. In one embodiment, a first appliance 200 communicateswith a second appliance 200′. In other embodiments, the appliance 200could be a part of any client 102 or server 106 on the same or differentnetwork 104,104′ as the client 102. One or more appliances 200 may belocated at any point in the network or network communications pathbetween a client 102 and a server 106.

In one embodiment, the system may include multiple, logically-groupedservers 106. In these embodiments, the logical group of servers may bereferred to as a server farm 38. In some of these embodiments, theserves 106 may be geographically dispersed. In some cases, a farm 38 maybe administered as a single entity. In other embodiments, the serverfarm 38 comprises a plurality of server farms 38. In one embodiment, theserver farm executes one or more applications on behalf of one or moreclients 102.

The servers 106 within each farm 38 can be heterogeneous. One or more ofthe servers 106 can operate according to one type of operating systemplatform (e.g., WINDOWS NT, manufactured by Microsoft Corp. of Redmond,Wash.), while one or more of the other servers 106 can operate onaccording to another type of operating system platform (e.g., Unix orLinux). The servers 106 of each farm 38 do not need to be physicallyproximate to another server 106 in the same farm 38. Thus, the group ofservers 106 logically grouped as a farm 38 may be interconnected using awide-area network (WAN) connection or medium-area network (MAN)connection. For example, a farm 38 may include servers 106 physicallylocated in different continents or different regions of a continent,country, state, city, campus, or room. Data transmission speeds betweenservers 106 in the farm 38 can be increased if the servers 106 areconnected using a local-area network (LAN) connection or some form ofdirect connection.

Servers 106 may be referred to as a file server, application server, webserver, proxy server, or gateway server. In some embodiments, a server106 may have the capacity to function as either an application server oras a master application server. In one embodiment, a server 106 mayinclude an Active Directory. The clients 102 may also be referred to asclient nodes or endpoints. In some embodiments, a client 102 has thecapacity to function as both a client node seeking access toapplications on a server and as an application server providing accessto hosted applications for other clients 102 a-102 n.

In some embodiments, a client 102 communicates with a server 106. In oneembodiment, the client 102 communicates directly with one of the servers106 in a farm 38. In another embodiment, the client 102 executes aprogram neighborhood application to communicate with a server 106 in afarm 38. In still another embodiment, the server 106 provides thefunctionality of a master node. In some embodiments, the client 102communicates with the server 106 in the farm 38 through a network 104.Over the network 104, the client 102 can, for example, request executionof various applications hosted by the servers 106 a-106 n in the farm 38and receive output of the results of the application execution fordisplay. In some embodiments, only the master node provides thefunctionality required to identify and provide address informationassociated with a server 106′ hosting a requested application.

In one embodiment, the server 106 provides functionality of a webserver. In another embodiment, the server 106 a receives requests fromthe client 102, forwards the requests to a second server 106 b andresponds to the request by the client 102 with a response to the requestfrom the server 106 b. In still another embodiment, the server 106acquires an enumeration of applications available to the client 102 andaddress information associated with a server 106 hosting an applicationidentified by the enumeration of applications. In yet anotherembodiment, the server 106 presents the response to the request to theclient 102 using a web interface. In one embodiment, the client 102communicates directly with the server 106 to access the identifiedapplication. In another embodiment, the client 102 receives applicationoutput data, such as display data, generated by an execution of theidentified application on the server 106.

Referring now to FIG. 1B, a network environment for delivering and/oroperating a computing environment on a client 102 is depicted. In someembodiments, a server 106 includes an application delivery system 190for delivering a computing environment or an application and/or datafile to one or more clients 102. In brief overview, a client 10 is incommunication with a server 106 via network 104, 104′ and appliance 200.For example, the client 102 may reside in a remote office of a company,e.g., a branch office, and the server 106 may reside at a corporate datacenter. The client 102 comprises a client agent 120, and a computingenvironment 15. The computing environment 15 may execute or operate anapplication that accesses, processes or uses a data file. The computingenvironment 15, application and/or data file may be delivered via theappliance 200 and/or the server 106.

In some embodiments, the appliance 200 accelerates delivery of acomputing environment 15, or any portion thereof, to a client 102. Inone embodiment, the appliance 200 accelerates the delivery of thecomputing environment 15 by the application delivery system 190. Forexample, the embodiments described herein may be used to acceleratedelivery of a streaming application and data file processable by theapplication from a central corporate data center to a remote userlocation, such as a branch office of the company. In another embodiment,the appliance 200 accelerates transport layer traffic between a client102 and a server 106. The appliance 200 may provide accelerationtechniques for accelerating any transport layer payload from a server106 to a client 102, such as: 1) transport layer connection pooling, 2)transport layer connection multiplexing, 3) transport control protocolbuffering, 4) compression and 5) caching. In some embodiments, theappliance 200 provides load balancing of servers 106 in responding torequests from clients 102. In other embodiments, the appliance 200 actsas a proxy or access server to provide access to the one or more servers106. In another embodiment, the appliance 200 provides a secure virtualprivate network connection from a first network 104 of the client 102 tothe second network 104′ of the server 106, such as an SSL VPNconnection. It yet other embodiments, the appliance 200 providesapplication firewall security, control and management of the connectionand communications between a client 102 and a server 106.

In some embodiments, the application delivery management system 190provides application delivery techniques to deliver a computingenvironment to a desktop of a user, remote or otherwise, based on aplurality of execution methods and based on any authentication andauthorization policies applied via a policy engine 195. With thesetechniques, a remote user may obtain a computing environment and accessto server stored applications and data files from any network connecteddevice 100. In one embodiment, the application delivery system 190 mayreside or execute on a server 106. In another embodiment, theapplication delivery system 190 may reside or execute on a plurality ofservers 106 a-106 n. In some embodiments, the application deliverysystem 190 may execute in a server farm 38. In one embodiment, theserver 106 executing the application delivery system 190 may also storeor provide the application and data file. In another embodiment, a firstset of one or more servers 106 may execute the application deliverysystem 190, and a different server 106 n may store or provide theapplication and data file. In some embodiments, each of the applicationdelivery system 190, the application, and data file may reside or belocated on different servers. In yet another embodiment, any portion ofthe application delivery system 190 may reside, execute or be stored onor distributed to the appliance 200, or a plurality of appliances.

The client 102 may include a computing environment 15 for executing anapplication that uses or processes a data file. The client 102 vianetworks 104, 104′ and appliance 200 may request an application and datafile from the server 106. In one embodiment, the appliance 200 mayforward a request from the client 102 to the server 106. For example,the client 102 may not have the application and data file stored oraccessible locally. In response to the request, the application deliverysystem 190 and/or server 106 may deliver the application and data fileto the client 102. For example, in one embodiment, the server 106 maytransmit the application as an application stream to operate incomputing environment 15 on client 102.

In some embodiments, the application delivery system 190 comprises anyportion of the Citrix Access Suite™ by Citrix Systems, Inc., such as theMetaFrame or Citrix Presentation Server™ and/or any of the Microsoft®Windows Terminal Services manufactured by the Microsoft Corporation. Inone embodiment, the application delivery system 190 may deliver one ormore applications to clients 102 or users via a remote-display protocolor otherwise via remote-based or server-based computing. In anotherembodiment, the application delivery system 190 may deliver one or moreapplications to clients or users via steaming of the application.

In one embodiment, the application delivery system 190 includes a policyengine 195 for controlling and managing the access to, selection ofapplication execution methods and the delivery of applications. In someembodiments, the policy engine 195 determines the one or moreapplications a user or client 102 may access. In another embodiment, thepolicy engine 195 determines how the application should be delivered tothe user or client 102, e.g., the method of execution. In someembodiments, the application delivery system 190 provides a plurality ofdelivery techniques from which to select a method of applicationexecution, such as a server-based computing, streaming or delivering theapplication locally to the client 102 for local execution.

In one embodiment, a client 102 requests execution of an applicationprogram and the application delivery system 190 comprising a server 106selects a method of executing the application program. In someembodiments, the server 106 receives credentials from the client 102. Inanother embodiment, the server 106 receives a request for an enumerationof available applications from the client 102. In one embodiment, inresponse to the request or receipt of credentials, the applicationdelivery system 190 enumerates a plurality of application programsavailable to the client 102. The application delivery system 190receives a request to execute an enumerated application. The applicationdelivery system 190 selects one of a predetermined number of methods forexecuting the enumerated application, for example, responsive to apolicy of a policy engine. The application delivery system 190 mayselect a method of execution of the application enabling the client 102to receive application-output data generated by execution of theapplication program on a server 106. The application delivery system 190may select a method of execution of the application enabling the localmachine 10 to execute the application program locally after retrieving aplurality of application files comprising the application. In yetanother embodiment, the application delivery system 190 may select amethod of execution of the application to stream the application via thenetwork 104 to the client 102.

A client 102 may execute, operate or otherwise provide an application,which can be any type and/or form of software, program, or executableinstructions such as any type and/or form of web browser, web-basedclient, client-server application, a thin-client computing client, anActiveX control, or a Java applet, or any other type and/or form ofexecutable instructions capable of executing on client 102. In someembodiments, the application may be a server-based or a remote-basedapplication executed on behalf of the client 102 on a server 106. In oneembodiments the server 106 may display output to the client 102 usingany thin-client or remote-display protocol, such as the IndependentComputing Architecture (ICA) protocol manufactured by Citrix Systems,Inc. of Ft. Lauderdale, Fla. or the Remote Desktop Protocol (RDP)manufactured by the Microsoft Corporation of Redmond, Wash. Theapplication can use any type of protocol and it can be, for example, anHTTP client, an FTP client, an Oscar client, or a Telnet client. Inother embodiments, the application comprises any type of softwarerelated to VoIP communications, such as a soft IP telephone. In furtherembodiments, the application comprises any application related toreal-time data communications, such as applications for streaming videoand/or audio.

In some embodiments, the server 106 or a server farm 38 may be runningone or more applications, such as an application providing a thin-clientcomputing or remote display presentation application. In one embodiment,the server 106 or server farm 38 executes as an application, any portionof the Citrix Access Suite™ by Citrix Systems, Inc., such as theMetaFrame or Citrix Presentation Server™, and/or any of the Microsoft®Windows Terminal Services manufactured by the Microsoft Corporation. Inone embodiment, the application is an ICA client, developed by CitrixSystems, Inc. of Fort Lauderdale, Fla. In other embodiments, theapplication includes a Remote Desktop (RDP) client, developed byMicrosoft Corporation of Redmond, Wash. Also, the server 106 may run anapplication, which for example, may be an application server providingemail services such as Microsoft Exchange manufactured by the MicrosoftCorporation of Redmond, Wash., a web or Internet server, or a desktopsharing server, or a collaboration server. In some embodiments, any ofthe applications may comprise any type of hosted service or products,such as GoToMeeting™ provided by Citrix Online Division, Inc. of SantaBarbara, Calif., WebEx™ provided by WebEx, Inc. of Santa Clara, Calif.,or Microsoft Office Live Meeting provided by Microsoft Corporation ofRedmond, Wash.

The client 102, server 106, and appliance 200 may be deployed as and/orexecuted on any type and form of computing device, such as a computer,network device or appliance capable of communicating on any type andform of network and performing the operations described herein. FIGS. 1Cand 1D depict block diagrams of a computing device 100 useful forpracticing an embodiment of the client 102, server 106 or appliance 200.As shown in FIGS. 1C and 1D, each computing device 100 includes acentral processing unit 101, and a main memory unit 122. As shown inFIG. 1C, a computing device 100 may include a visual display device 124,a keyboard 126 and/or a pointing device 127, such as a mouse. Eachcomputing device 100 may also include additional optional elements, suchas one or more input/output devices 130 a-130 b (generally referred tousing reference numeral 130), and a cache memory 140 in communicationwith the central processing unit 101.

The central processing unit 101 is any logic circuitry that responds toand processes instructions fetched from the main memory unit 122. Inmany embodiments, the central processing unit is provided by amicroprocessor unit, such as: those manufactured by Intel Corporation ofMountain View, Calif.; those manufactured by Motorola Corporation ofSchaumburg, Ill.; those manufactured by Transmeta Corporation of SantaClara, Calif.; the RS/6000 processor, those manufactured byInternational Business Machines of White Plains, N.Y.; or thosemanufactured by Advanced Micro Devices of Sunnyvale, Calif. Thecomputing device 100 may be based on any of these processors, or anyother processor capable of operating as described herein.

Main memory unit 122 may be one or more memory chips capable of storingdata and allowing any storage location to be directly accessed by themicroprocessor 101, such as Static random access memory (SRAM), BurstSRAM or SynchBurst SRAM (BSRAM), Dynamic random access memory (DRAM),Fast Page Mode DRAM (FPM DRAM), Enhanced DRAM (EDRAM), Extended DataOutput RAM (EDO RAM), Extended Data Output DRAM (EDO DRAM), BurstExtended Data Output DRAM (BEDO DRAM), Enhanced DRAM (EDRAM),synchronous DRAM (SDRAM), JEDEC SRAM, PC100 SDRAM, Double Data RateSDRAM (DDR SDRAM), Enhanced SDRAM (ESDRAM), SyncLink DRAM (SLDRAM),Direct Rambus DRAM (DRDRAM), or Ferroelectric RAM (FRAM). The mainmemory 122 may be based on any of the above described memory chips, orany other available memory chips capable of operating as describedherein. In the embodiment shown in FIG. 1C, the processor 101communicates with main memory 122 via a system bus 150 (described inmore detail below). FIG. 1C depicts an embodiment of a computing device100 in which the processor communicates directly with main memory 122via a memory port 103. For example, in FIG. 1D the main memory 122 maybe DRDRAM.

FIG. 1D depicts an embodiment in which the main processor 101communicates directly with cache memory 140 via a secondary bus,sometimes referred to as a backside bus. In other embodiments, the mainprocessor 101 communicates with cache memory 140 using the system bus150. Cache memory 140 typically has a faster response time than mainmemory 122 and is typically provided by SRAM, BSRAM, or EDRAM. In theembodiment shown in FIG. 1C, the processor 101 communicates with variousI/O devices 130 via a local system bus 150. Various busses may be usedto connect the central processing unit 101 to any of the I/O devices130, including a VESA VL bus, an ISA bus, an EISA bus, a MicroChannelArchitecture (MCA) bus, a PCI bus, a PCI-X bus, a PCI-Express bus, or aNuBus. For embodiments in which the I/O device is a video display 124,the processor 101 may use an Advanced Graphics Port (AGP) to communicatewith the display 124. FIG. 1D depicts an embodiment of a computer 100 inwhich the main processor 101 communicates directly with I/O device 130via HyperTransport, Rapid I/O, or InfiniBand. FIG. 1D also depicts anembodiment in which local busses and direct communication are mixed: theprocessor 101 communicates with I/O device 130 using a localinterconnect bus while communicating with I/O device 130 directly.

The computing device 100 may support any suitable installation device116, such as a floppy disk drive for receiving floppy disks such as3.5-inch, 5.25-inch disks or ZIP disks, a CD-ROM drive, a CD-R/RW drive,a DVD-ROM drive, tape drives of various formats, USB device, hard-driveor any other device suitable for installing software and programs suchas any client agent 120, or portion thereof. The computing device 100may further comprise a storage device 128, such as one or more hard diskdrives or redundant arrays of independent disks, for storing anoperating system and other related software, and for storing applicationsoftware programs such as any program related to the client agent 120.Optionally, any of the installation devices 116 could also be used asthe storage device 128. Additionally, the operating system and thesoftware can be run from a bootable medium, for example, a bootable CD,such as KNOPPIX®, a bootable CD for GNU/Linux that is available as aGNU/Linux distribution from knoppix.net.

Furthermore, the computing device 100 may include a network interface118 to interface to a Local Area Network (LAN), Wide Area Network (WAN)or the Internet through a variety of connections including, but notlimited to, standard telephone lines, LAN or WAN links (e.g., 802.11,T1, T3, 56kb, X.25), broadband connections (e.g., ISDN, Frame Relay,ATM), wireless connections, or some combination of any or all of theabove. The network interface 118 may comprise a built-in networkadapter, network interface card, PCMCIA network card, card bus networkadapter, wireless network adapter, USB network adapter, modem or anyother device suitable for interfacing the computing device 100 to anytype of network capable of communication and performing the operationsdescribed herein. A wide variety of I/O devices 130 a-130 n may bepresent in the computing device 100. Input devices include keyboards,mice, trackpads, trackballs, microphones, and drawing tablets. Outputdevices include video displays, speakers, inkjet printers, laserprinters, and dye-sublimation printers. The I/O devices 130 may becontrolled by an I/O controller 123 as shown in FIG. 1C. The I/Ocontroller may control one or more I/O devices such as a keyboard 126and a pointing device 127, e.g., a mouse or optical pen. Furthermore, anI/O device may also provide storage 128 and/or an installation medium116 for the computing device 100. In still other embodiments, thecomputing device 100 may provide USB connections to receive handheld USBstorage devices such as the USB Flash Drive line of devices manufacturedby Twintech Industry, Inc. of Los Alamitos, Calif.

In some embodiments, the computing device 100 may comprise or beconnected to multiple display devices 124 a-124 n, which each may be ofthe same or different type and/or form. As such, any of the I/O devices130 a-130 n and/or the I/O controller 123 may comprise any type and/orform of suitable hardware, software, or combination of hardware andsoftware to support, enable or provide for the connection and use ofmultiple display devices 124 a-124 n by the computing device 100. Forexample, the computing device 100 may include any type and/or form ofvideo adapter, video card, driver, and/or library to interface,communicate, connect or otherwise use the display devices 124 a-124 n.In one embodiment, a video adapter may comprise multiple connectors tointerface to multiple display devices 124 a-124 n. In other embodiments,the computing device 100 may include multiple video adapters, with eachvideo adapter connected to one or more of the display devices 124 a-124n. In some embodiments, any portion of the operating system of thecomputing device 100 may be configured for using multiple displays 124a-124 n. In other embodiments, one or more of the display devices 124a-124 n may be provided by one or more other computing devices, such ascomputing devices 100 a and 100 b connected to the computing device 100,for example, via a network. These embodiments may include any type ofsoftware designed and constructed to use another computer's displaydevice as a second display device 124 a for the computing device 100.One ordinarily skilled in the art will recognize and appreciate thevarious ways and embodiments that a computing device 100 may beconfigured to have multiple display devices 124 a-124 n.

In further embodiments, an I/O device 130 may be a bridge 170 betweenthe system bus 150 and an external communication bus, such as a USB bus,an Apple Desktop Bus, an RS-232 serial connection, a SCSI bus, aFireWire bus, a FireWire 800 bus, an Ethernet bus, an AppleTalk bus, aGigabit Ethernet bus, an Asynchronous Transfer Mode bus, a HIPPI bus, aSuper HIPPI bus, a SerialPlus bus, a SCI/LAMP bus, a FibreChannel bus,or a Serial Attached small computer system interface bus.

A computing device 100 of the sort depicted in FIGS. 1C and 1D typicallyoperate under the control of operating systems, which control schedulingof tasks and access to system resources. The computing device 100 can berunning any operating system such as any of the versions of theMicrosoft® Windows operating systems, the different releases of the Unixand Linux operating systems, any version of the Mac OS® for Macintoshcomputers, any embedded operating system, any real-time operatingsystem, any open source operating system, any proprietary operatingsystem, any operating systems for mobile computing devices, or any otheroperating system capable of running on the computing device andperforming the operations described herein. Typical operating systemsinclude: WINDOWS 3.x, WINDOWS 95, WINDOWS 98, WINDOWS 2000, WINDOWS NT3.51, WINDOWS NT 4.0, WINDOWS CE, and WINDOWS XP, all of which aremanufactured by Microsoft Corporation of Redmond, Wash.; MacOS,manufactured by Apple Computer of Cupertino, Calif.; OS/2, manufacturedby International Business Machines of Armonk, N.Y.; and Linux, afreely-available operating system distributed by Caldera Corp. of SaltLake City, Utah, or any type and/or form of a Unix operating system,among others.

In other embodiments, the computing device 100 may have differentprocessors, operating systems, and input devices consistent with thedevice. For example, in one embodiment the computer 100 is a Treo 180,270, 1060, 600 or 650 smart phone manufactured by Palm, Inc. In thisembodiment, the Treo smart phone is operated under the control of thePalmOS operating system and includes a stylus input device as well as afive-way navigator device. Moreover, the computing device 100 can be anyworkstation, desktop computer, laptop or notebook computer, server,handheld computer, mobile telephone, any other computer, or other formof computing or telecommunications device that is capable ofcommunication and that has sufficient processor power and memorycapacity to perform the operations described herein.

B. Appliance Architecture

FIG. 2A illustrates an example embodiment of the appliance 200. Thearchitecture of the appliance 200 in FIG. 2A is provided by way ofillustration only and is not intended to be limiting. As shown in FIG.2, appliance 200 comprises a hardware layer 206 and a software layerdivided into a user space 202 and a kernel space 204.

Hardware layer 206 provides the hardware elements upon which programsand services within kernel space 204 and user space 202 are executed.Hardware layer 206 also provides the structures and elements which allowprograms and services within kernel space 204 and user space 202 tocommunicate data both internally and externally with respect toappliance 200. As shown in FIG. 2, the hardware layer 206 includes aprocessing unit 262 for executing software programs and services, amemory 264 for storing software and data, network ports 266 fortransmitting and receiving data over a network, and an encryptionprocessor 260 for performing functions related to Secure Sockets Layerprocessing of data transmitted and received over the network. In someembodiments, the central processing unit 262 may perform the functionsof the encryption processor 260 in a single processor. Additionally, thehardware layer 206 may comprise multiple processors for each of theprocessing unit 262 and the encryption processor 260. The processor 262may include any of the processors 101 described above in connection withFIGS. 1C and 1D. In some embodiments, the central processing unit 262may perform the functions of the encryption processor 260 in a singleprocessor. Additionally, the hardware layer 206 may comprise multipleprocessors for each of the processing unit 262 and the encryptionprocessor 260. For example, in one embodiment, the appliance 200comprises a first processor 262 and a second processor 262′. In otherembodiments, the processor 262 or 262′ comprises a multi-core processor.

Although the hardware layer 206 of appliance 200 is generallyillustrated with an encryption processor 260, processor 260 may be aprocessor for performing functions related to any encryption protocol,such as the Secure Socket Layer (SSL) or Transport Layer Security (TLS)protocol. In some embodiments, the processor 260 may be a generalpurpose processor (GPP), and in further embodiments, may be haveexecutable instructions for performing processing of any securityrelated protocol.

Although the hardware layer 206 of appliance 200 is illustrated withcertain elements in FIG. 2, the hardware portions or components ofappliance 200 may comprise any type and form of elements, hardware orsoftware, of a computing device, such as the computing device 100illustrated and discussed herein in conjunction with FIGS. 1C and 1D. Insome embodiments, the appliance 200 may comprise a server, gateway,router, switch, bridge or other type of computing or network device, andhave any hardware and/or software elements associated therewith.

The operating system of appliance 200 allocates, manages, or otherwisesegregates the available system memory into kernel space 204 and userspace 204. In example software architecture 200, the operating systemmay be any type and/or form of Unix operating system although theinvention is not so limited. As such, the appliance 200 can be runningany operating system such as any of the versions of the Microsoft®Windows operating systems, the different releases of the Unix and Linuxoperating systems, any version of the Mac OS® for Macintosh computers,any embedded operating system, any network operating system, anyreal-time operating system, any open source operating system, anyproprietary operating system, any operating systems for mobile computingdevices or network devices, or any other operating system capable ofrunning on the appliance 200 and performing the operations describedherein.

The kernel space 204 is reserved for running the kernel 230, includingany device drivers, kernel extensions or other kernel related software.As known to those skilled in the art, the kernel 230 is the core of theoperating system, and provides access, control, and management ofresources and hardware-related elements of the application 104. Inaccordance with an embodiment of the appliance 200, the kernel space 204also includes a number of network services or processes working inconjunction with a cache manager 232. sometimes also referred to as theintegrated cache, the benefits of which are described in detail furtherherein. Additionally, the embodiment of the kernel 230 will depend onthe embodiment of the operating system installed, configured, orotherwise used by the device 200.

In one embodiment, the device 200 comprises one network stack 267, suchas a TCP/IP based stack, for communicating with the client 102 and/orthe server 106. In one embodiment, the network stack 267 is used tocommunicate with a first network, such as network 108, and a secondnetwork 110. In some embodiments, the device 200 terminates a firsttransport layer connection, such as a TCP connection of a client 102,and establishes a second transport layer connection to a server 106 foruse by the client 102, e.g., the second transport layer connection isterminated at the appliance 200 and the server 106. The first and secondtransport layer connections may be established via a single networkstack 267. In other embodiments, the device 200 may comprise multiplenetwork stacks, for example 267 and 267′, and the first transport layerconnection may be established or terminated at one network stack 267,and the second transport layer connection on the second network stack267′. For example, one network stack may be for receiving andtransmitting network packet on a first network, and another networkstack for receiving and transmitting network packets on a secondnetwork. In one embodiment, the network stack 267 comprises a buffer 243for queuing one or more network packets for transmission by theappliance 200.

As shown in FIG. 2, the kernel space 204 includes the cache manager 232,a high-speed layer 2-7 integrated packet engine 240, an encryptionengine 234, a policy engine 236 and multi-protocol compression logic238. Running these components or processes 232, 240, 234, 236 and 238 inkernel space 204 or kernel mode instead of the user space 202 improvesthe performance of each of these components, alone and in combination.Kernel operation means that these components or processes 232, 240, 234,236 and 238 run in the core address space of the operating system of thedevice 200. For example, running the encryption engine 234 in kernelmode improves encryption performance by moving encryption and decryptionoperations to the kernel, thereby reducing the number of transitionsbetween the memory space or a kernel thread in kernel mode and thememory space or a thread in user mode. For example, data obtained inkernel mode may not need to be passed or copied to a process or threadrunning in user mode, such as from a kernel level data structure to auser level data structure. In another aspect, the number of contextswitches between kernel mode and user mode are also reduced.Additionally, synchronization of and communications between any of thecomponents or processes 232, 240, 235, 236 and 238 can be performed moreefficiently in the kernel space 204.

In some embodiments, any portion of the components 232, 240, 234, 236and 238 may run or operate in the kernel space 204, while other portionsof these components 232, 240, 234, 236 and 238 may run or operate inuser space 202. In one embodiment, the appliance 200 uses a kernel-leveldata structure providing access to any portion of one or more networkpackets, for example, a network packet comprising a request from aclient 102 or a response from a server 106. In some embodiments, thekernel-level data structure may be obtained by the packet engine 240 viaa transport layer driver interface or filter to the network stack 267.The kernel-level data structure may comprise any interface and/or dataaccessible via the kernel space 204 related to the network stack 267,network traffic or packets received or transmitted by the network stack267. In other embodiments, the kernel-level data structure may be usedby any of the components or processes 232, 240, 234, 236 and 238 toperform the desired operation of the component or process. In oneembodiment, a component 232, 240, 234, 236 and 238 is running in kernelmode 204 when using the kernel-level data structure, while in anotherembodiment, the component 232, 240, 234, 236 and 238 is running in usermode when using the kernel-level data structure. In some embodiments,the kernel-level data structure may be copied or passed to a secondkernel-level data structure, or any desired user-level data structure.

The cache manager 232 may comprise software, hardware or any combinationof software and hardware to provide cache access, control and managementof any type and form of content, such as objects or dynamicallygenerated objects served by the originating servers 106. The data,objects or content processed and stored by the cache manager 232 maycomprise data in any format, such as a markup language, or communicatedvia any protocol. In some embodiments, the cache manager 232 duplicatesoriginal data stored elsewhere or data previously computed, generated ortransmitted, in which the original data may require longer access timeto fetch, compute or otherwise obtain relative to reading a cache memoryelement. Once the data is stored in the cache memory element, future usecan be made by accessing the cached copy rather than refetching orrecomputing the original data, thereby reducing the access time. In someembodiments, the cache memory element nat comprise a data object inmemory 264 of device 200. In other embodiments, the cache memory elementmay comprise memory having a faster access time than memory 264. Inanother embodiment, the cache memory element may comprise any type andform of storage element of the device 200, such as a portion of a harddisk. In some embodiments, the processing unit 262 may provide cachememory for use by the cache manager 232. In yet further embodiments, thecache manager 232 may use any portion and combination of memory,storage, or the processing unit for caching data, objects, and othercontent.

Furthermore, the cache manager 232 includes any logic, functions, rules,or operations to perform any embodiments of the techniques of theappliance 200 described herein. For example, the cache manager 232includes logic or functionality to invalidate objects based on theexpiration of an invalidation time period or upon receipt of aninvalidation command from a client 102 or server 106. In someembodiments, the cache manager 232 may operate as a program, service,process or task executing in the kernel space 204, and in otherembodiments, in the user space 202. In one embodiment, a first portionof the cache manager 232 executes in the user space 202 while a secondportion executes in the kernel space 204. In some embodiments, the cachemanager 232 can comprise any type of general purpose processor (GPP), orany other type of integrated circuit, such as a Field Programmable GateArray (FPGA), Programmable Logic Device (PLD), or Application SpecificIntegrated Circuit (ASIC).

The policy engine 236 may include, for example, an intelligentstatistical engine or other programmable application(s). In oneembodiment, the policy engine 236 provides a configuration mechanism toallow a user to identifying, specify, define or configure a cachingpolicy. Policy engine 236, in some embodiments, also has access tomemory to support data structures such as lookup tables or hash tablesto enable user-selected caching policy decisions. In other embodiments,the policy engine 236 may comprise any logic, rules, functions oroperations to determine and provide access, control and management ofobjects, data or content being cached by the appliance 200 in additionto access, control and management of security, network traffic, networkaccess, compression or any other function or operation performed by theappliance 200. Further examples of specific caching policies are furtherdescribed herein.

The encryption engine 234 comprises any logic, business rules, functionsor operations for handling the processing of any security relatedprotocol, such as SSL or TLS, or any function related thereto. Forexample, the encryption engine 234 encrypts and decrypts networkpackets, or any portion thereof, communicated via the appliance 200. Theencryption engine 234 may also setup or establish SSL or TLS connectionson behalf of the client 102 a-102 n, server 106 a-106 n, or appliance200. As such, the encryption engine 234 provides offloading andacceleration of SSL processing. In one embodiment, the encryption engine234 uses a tunneling protocol to provide a virtual private networkbetween a client 102 a-102 n and a server 106 a-106 n. In someembodiments, the encryption engine 234 is in communication with theEncryption processor 260. In other embodiments, the encryption engine234 comprises executable instructions running on the Encryptionprocessor 260.

The multi-protocol compression engine 238 comprises any logic, businessrules, function or operations for compressing one or more protocols of anetwork packet, such as any of the protocols used by the network stack267 of the device 200. In one embodiment, multi-protocol compressionengine 238 compresses bi-directionally between clients 102 a-102 n andservers 106 a-106 n any TCP/IP based protocol, including MessagingApplication Programming Interface (MAPI) (email), File Transfer Protocol(FTP), HyperText Transfer Protocol (HTTP), Common Internet File System(CIFS) protocol (file transfer), Independent Computing Architecture(ICA) protocol, Remote Desktop Protocol (RDP), Wireless ApplicationProtocol (WAP), Mobile IP protocol, and Voice Over IP (VoIP) protocol.In other embodiments, multi-protocol compression engine 238 providescompression of Hypertext Markup Language (HTML) based protocols and insome embodiments, provides compression of any markup languages, such asthe Extensible Markup Language (XML). In one embodiment, themulti-protocol compression engine 238 provides compression of anyhigh-performance protocol, such as any protocol designed for appliance200 to appliance 200 communications. In another embodiment, themulti-protocol compression engine 238 compresses any payload of or anycommunication using a modified transport control protocol, such asTransaction TCP (T/TCP), TCP with selection acknowledgements (TCP-SACK),TCP with large windows (TCP-LW), a congestion prediction protocol suchas the TCP-Vegas protocol, and a TCP spoofing protocol.

As such, the multi-protocol compression engine 238 acceleratesperformance for users accessing applications via desktop clients, e.g.,Microsoft Outlook and non-Web thin clients, such as any client launchedby popular enterprise applications like Oracle, SAP and Siebel, and evenmobile clients, such as the Pocket PC. In some embodiments, themulti-protocol compression engine 238 by executing in the kernel mode204 and integrating with packet processing engine 240 accessing thenetwork stack 267 is able to compress any of the protocols carried bythe TCP/IP protocol, such as any application layer protocol.

High speed layer 2-7 integrated packet engine 240, also generallyreferred to as a packet processing engine or packet engine, isresponsible for managing the kernel-level processing of packets receivedand transmitted by appliance 200 via network ports 266. The high speedlayer 2-7 integrated packet engine 240 may comprise a buffer for queuingone or more network packets during processing, such as for receipt of anetwork packet or transmission of a network packer. Additionally, thehigh speed layer 2-7 integrated packet engine 240 is in communicationwith one or more network stacks 267 to send and receive network packetsvia network ports 266. The high speed layer 2-7 integrated packet engine240 works in conjunction with encryption engine 234, cache manager 232,policy engine 236 and multi-protocol compression logic 238. Inparticular, encryption engine 234 is configured to perform SSLprocessing of packets, policy engine 236 is configured to performfunctions related to traffic management such as request-level contentswitching and request-level cache redirection, and multi-protocolcompression logic 238 is configured to perform functions related tocompression and decompression of data.

The high speed layer 2-7 integrated packet engine 240 includes a packetprocessing timer 242. In one embodiment, the packet processing timer 242provides one or more time intervals to trigger the processing ofincoming, i.e., received, or outgoing, i.e., transmitted, networkpackets. In some embodiments, the high speed layer 2-7 integrated packetengine 240 processes network packets responsive to the timer 242. Thepacket processing timer 242 provides any type and form of signal to thepacket engine 240 to notify, trigger, or communicate a time relatedevent, interval or occurrence. In many embodiments, the packetprocessing timer 242 operates in the order of milliseconds, such as forexample 100 ms, 50 ms or 25 ms. For example, in some embodiments, thepacket processing timer 242 provides time intervals or otherwise causesa network packet to be processed by the high speed layer 2-7 integratedpacket engine 240 at a 10 ms time interval, while in other embodiments,at a 5 ms time interval, and still yet in further embodiments, as shortas a 3, 2, or 1 ms time interval. The high speed layer 2-7 integratedpacket engine 240 may be interfaced, integrated or in communication withthe encryption engine 234, cache manager 232, policy engine 236 andmulti-protocol compression engine 238 during operation. As such, any ofthe logic, functions, or operations of the encryption engine 234, cachemanager 232, policy engine 236 and multi-protocol compression logic 238may be performed responsive to the packet processing timer 242 and/orthe packet engine 240. Therefore, any of the logic, functions, oroperations of the encryption engine 234, cache manager 232, policyengine 236 and multi-protocol compression logic 238 may be performed atthe granularity of time intervals provided via the packet processingtimer 242, for example, at a time interval of less than or equal to 10ms. For example, in one embodiment, the cache manager 232 may performinvalidation of any cached objects responsive to the high speed layer2-7 integrated packet engine 240 and/or the packet processing timer 242.In another embodiment, the expiry or invalidation time of a cachedobject can be set to the same order of granularity as the time intervalof the packet processing timer 242, such as at every 10 ms.

In contrast to kernel space 204, user space 202 is the memory area orportion of the operating system used by user mode applications orprograms otherwise running in user mode. A user mode application may notaccess kernel space 204 directly and uses service calls in order toaccess kernel services. As shown in FIG. 2, user space 202 of appliance200 includes a graphical user interface (GUI) 210, a command lineinterface (CLI) 212, shell services 214, health monitoring program 216,and daemon services 218. GUI 210 and CLI 212 provide a means by which asystem administrator or other user can interact with and control theoperation of appliance 200, such as via the operating system of theappliance 200 and either is user space 202 or kernel space 204. The GUI210 may be any type and form of graphical user interface and may bepresented via text, graphical or otherwise, by any type of program orapplication, such as a browser. The CLI 212 may be any type and form ofcommand line or text-based interface, such as a command line provided bythe operating system. For example, the CLI 212 may comprise a shell,which is a tool to enable users to interact with the operating system.In some embodiments, the CLI 212 may be provided via a bash, csh, tcsh,or ksh type shell. The shell services 214 comprises the programs,services, tasks, processes or executable instructions to supportinteraction with the appliance 200 or operating system by a user via theGUI 210 and/or CLI 212.

Health monitoring program 216 is used to monitor, check, report andensure that network systems are functioning properly and that users arereceiving requested content over a network. Health monitoring program216 comprises one or more programs, services, tasks, processes orexecutable instructions to provide logic, rules, functions or operationsfor monitoring any activity of the appliance 200. In some embodiments,the health monitoring program 216 intercepts and inspects any networktraffic passed via the appliance 200. In other embodiments, the healthmonitoring program 216 interfaces by any suitable means and/ormechanisms with one or more of the following: the encryption engine 234,cache manager 232, policy engine 236, multi-protocol compression logic238, packet engine 240, daemon services 218, and shell services 214. Assuch, the health monitoring program 216 may call any applicationprogramming interface (API) to determine a state, status, or health ofany portion of the appliance 200. For example, the health monitoringprogram 216 may ping or send a status inquiry on a periodic basis tocheck if a program, process, service or task is active and currentlyrunning In another example, the health monitoring program 216 may checkany status, error or history logs provided by any program, process,service or task to determine any condition, status or error with anyportion of the appliance 200.

Daemon services 218 are programs that run continuously or in thebackground and handle periodic service requests received by appliance200. In some embodiments, a daemon service may forward the requests toother programs or processes, such as another daemon service 218 asappropriate. As known to those skilled in the art, a daemon service 218may run unattended to perform continuous or periodic system widefunctions, such as network control, or to perform any desired task. Insome embodiments, one or more daemon services 218 run in the user space202, while in other embodiments, one or more daemon services 218 run inthe kernel space.

Referring now to FIG. 2B, another embodiment of the appliance 200 isdepicted. In brief overview, the appliance 200 provides one or more ofthe following services, functionality or operations: SSL VPNconnectivity 280, switching/load balancing 284, Domain Name Serviceresolution 286, acceleration 288 and an application firewall 290 forcommunications between one or more clients 102 and one or more servers106. In one embodiment, the appliance 200 comprises any of the networkdevices manufactured by Citrix Systems, Inc. of Ft. Lauderdale Fla.,referred to as Citrix NetScaler devices. Each of the servers 106 mayprovide one or more network related services 270 a-270 n (referred to asservices 270). For example, a server 106 may provide an http service270. The appliance 200 comprises one or more virtual servers or virtualinternet protocol servers, referred to as a vServer, VIP server, or justVIP 275 a-275 n (also referred herein as vServer 275). The vServer 275receives, intercepts or otherwise processes communications between aclient 102 and a server 106 in accordance with the configuration andoperations of the appliance 200.

The vServer 275 may comprise software, hardware or any combination ofsoftware and hardware. The vServer 275 may comprise any type and form ofprogram, service, task, process or executable instructions operating inuser mode 202, kernel mode 204 or any combination thereof in theappliance 200. The vServer 275 includes any logic, functions, rules, oroperations to perform any embodiments of the techniques describedherein, such as SSL VPN 280, switching/load balancing 284, Domain NameService resolution 286, acceleration 288 and an application firewall290. In some embodiments, the vServer 275 establishes a connection to aservice 270 of a server 106. The service 275 may comprise any program,application, process, task or set of executable instructions capable ofconnecting to and communicating to the appliance 200, client 102 orvServer 275. For example, the service 275 may comprise a web server,http server, ftp, email or database server. In some embodiments, theservice 270 is a daemon process or network driver for listening,receiving and/or sending communications for an application, such asemail, database or an enterprise application. In some embodiments, theservice 270 may communicate on a specific IP address, or IP address andport.

In some embodiments, the vServer 275 applies one or more policies of thepolicy engine 236 to network communications between the client 102 andserver 106. In one embodiment, the policies are associated with aVServer 275. In another embodiment, the policies are based on a user, ora group of users. In yet another embodiment, a policy is global andapplies to one or more vServers 275 a-275 n, and any user or group ofusers communicating via the appliance 200. In some embodiments, thepolicies of the policy engine have conditions upon which the policy isapplied based on any content of the communication, such as internetprotocol address, port, protocol type, header or fields in a packet, orthe context of the communication, such as user, group of the user,vServer 275, transport layer connection, and/or identification orattributes of the client 102 or server 106.

In other embodiments, the appliance 200 communicates or interfaces withthe policy engine 236 to determine authentication and/or authorizationof a remote user or a remote client 102 to access the computingenvironment 15, application, and/or data file from a server 106. Inanother embodiment, the appliance 200 communicates or interfaces withthe policy engine 236 to determine authentication and/or authorizationof a remote user or a remote client 102 to have the application deliverysystem 190 deliver one or more of the computing environment 15,application, and/or data file. In yet another embodiment, the appliance200 establishes a VPN or SSL VPN connection based on the policy engine's236 authentication and/or authorization of a remote user or a remoteclient 103 In one embodiment, the appliance 102 controls the flow ofnetwork traffic and communication sessions based on policies of thepolicy engine 236. For example, the appliance 200 may control the accessto a computing environment 15, application or data file based on thepolicy engine 236.

In some embodiments, the vServer 275 establishes a transport layerconnection, such as a TCP or UDP connection with a client 102 via theclient agent 120. In one embodiment, the vServer 275 listens for andreceives communications from the client 102. In other embodiments, thevServer 275 establishes a transport layer connection, such as a TCP orUDP connection with a client server 106. In one embodiment, the vServer275 establishes the transport layer connection to an internet protocoladdress and port of a server 270 running on the server 106. In anotherembodiment, the vServer 275 associates a first transport layerconnection to a client 102 with a second transport layer connection tothe server 106. In some embodiments, a vServer 275 establishes a pool oftransport layer connections to a server 106 and multiplexes clientrequests via the pooled transport layer connections.

In some embodiments, the appliance 200 provides a SSL VPN connection 280between a client 102 and a server 106. For example, a client 102 on afirst network 102 requests to establish a connection to a server 106 ona second network 104′. In some embodiments, the second network 104′ isnot routable from the first network 104. In other embodiments, theclient 102 is on a public network 104 and the server 106 is on a privatenetwork 104′, such as a corporate network. In one embodiment, the clientagent 120 intercepts communications of the client 102 on the firstnetwork 104, encrypts the communications, and transmits thecommunications via a first transport layer connection to the appliance200. The appliance 200 associates the first transport layer connectionon the first network 104 to a second transport layer connection to theserver 106 on the second network 104. The appliance 200 receives theintercepted communication from the client agent 120, decrypts thecommunications, and transmits the communication to the server 106 on thesecond network 104 via the second transport layer connection. The secondtransport layer connection may be a pooled transport layer connection.As such, the appliance 200 provides an end-to-end secure transport layerconnection for the client 102 between the two networks 104, 104′.

In one embodiment, the appliance 200 hosts an intranet internet protocolor intranetIP 282 address of the client 102 on the virtual privatenetwork 104. The client 102 has a local network identifier, such as aninternet protocol (IP) address and/or host name on the first network104. When connected to the second network 104′ via the appliance 200,the appliance 200 establishes, assigns or otherwise provides anIntranetIP, which is a network identifier, such as IP address and/orhost name, for the client 102 on the second network 104′. The appliance200 listens for and receives on the second or private network 104′ forany communications directed towards the client 102 using the client'sestablished IntranetIP 282. In one embodiment, the appliance 200 acts asor on behalf of the client 102 on the second private network 104. Forexample, in another embodiment, a vServer 275 listens for and respondsto communications to the IntranetIP 282 of the client 102. In someembodiments, if a computing device 100 on the second network 104′transmits a request, the appliance 200 processes the request as if itwere the client 102. For example, the appliance 200 may respond to aping to the client's IntranetIP 282. In another example, the appliancemay establish a connection, such as a TCP or UDP connection, withcomputing device 100 on the second network 104 requesting a connectionwith the client's IntranetIP 282.

In some embodiments, the appliance 200 provides one or more of thefollowing acceleration techniques 288 to communications between theclient 102 and server 106: 1) compression; 2) decompression; 3)Transmission Control Protocol pooling; 4) Transmission Control Protocolmultiplexing; 5) Transmission Control Protocol buffering; and 6)caching. In one embodiment, the appliance 200 relieves servers 106 ofmuch of the processing load caused by repeatedly opening and closingtransport layers connections to clients 102 by opening one or moretransport layer connections with each server 106 and maintaining theseconnections to allow repeated data accesses by clients via the Internet.This technique is referred to herein as “connection pooling”.

In some embodiments, in order to seamlessly splice communications from aclient 102 to a server 106 via a pooled transport layer connection, theappliance 200 translates or multiplexes communications by modifyingsequence number and acknowledgment numbers at the transport layerprotocol level. This is referred to as “connection multiplexing”. Insome embodiments, no application layer protocol interaction is required.For example, in the case of an in-bound packet (that is, a packetreceived from a client 102), the source network address of the packet ischanged to that of an output port of appliance 200, and the destinationnetwork address is changed to that of the intended server. In the caseof an outbound packet (that is, one received from a server 106), thesource network address is changed from that of the server 106 to that ofan output port of appliance 200 and the destination address is changedfrom that of appliance 200 to that of the requesting client 102. Thesequence numbers and acknowledgment numbers of the packet are alsotranslated to sequence numbers and acknowledgement expected by theclient 102 on the appliance's 200 transport layer connection to theclient 102. In some embodiments, the packet checksum of the transportlayer protocol is recalculated to account for these translations.

In another embodiment, the appliance 200 provides switching orload-balancing functionality 284 for communications between the client102 and server 106. In some embodiments, the appliance 200 distributestraffic and directs client requests to a server 106 based on layer 4 orapplication-layer request data. In one embodiment, although the networklayer or layer 2 of the network packet identifies a destination server106, the appliance 200 determines the server 106 to distribute thenetwork packet by application information and data carried as payload ofthe transport layer packet. In one embodiment, the health monitoringprograms 216 of the appliance 200 monitor the health of servers todetermine the server 106 for which to distribute a client's request. Insome embodiments, if the appliance 200 detects a server 106 is notavailable or has a load over a predetermined threshold, the appliance200 can direct or distribute client requests to another server 106.

In some embodiments, the appliance 200 acts as a Domain Name Service(DNS) resolver or otherwise provides resolution of a DNS request fromclients 102. In some embodiments, the appliance intercepts' a DNSrequest transmitted by the client 102. In one embodiment, the appliance200 responds to a client's DNS request with an IP address of or hostedby the appliance 200. In this embodiment, the client 102 transmitsnetwork communication for the domain name to the appliance 200. Inanother embodiment, the appliance 200 responds to a client's DNS requestwith an IP address of or hosted by a second appliance 200′. In someembodiments, the appliance 200 responds to a client's DNS request withan IP address of a server 106 determined by the appliance 200.

In yet another embodiment, the appliance 200 provides applicationfirewall functionality 290 for communications between the client 102 andserver 106. In one embodiment, the policy engine 236 provides rules fordetecting and blocking illegitimate requests. In some embodiments, theapplication firewall 290 protects against denial of service (DoS)attacks. In other embodiments, the appliance inspects the content ofintercepted requests to identify and block application-based attacks. Insome embodiments, the rules/policy engine 236 comprises one or moreapplication firewall or security control policies for providingprotections against various classes and types of web or Internet basedvulnerabilities, such as one or more of the following: 1) bufferoverflow, 2) CGI-BIN parameter manipulation, 3) form/hidden fieldmanipulation, 4) forceful browsing, 5) cookie or session poisoning, 6)broken access control list (ACLs) or weak passwords, 7) cross-sitescripting (XSS), 8) command injection, 9) SQL injection, 10) errortriggering sensitive information leak, 11) insecure use of cryptography,12) server misconfiguration, 13) back doors and debug options, 14)website defacement, 15) platform or operating systems vulnerabilities,and 16) zero-day exploits. In an embodiment, the application firewall290 provides HTML form field protection in the form of inspecting oranalyzing the network communication for one or more of the following: 1)required fields are returned, 2) no added field allowed, 3) read-onlyand hidden field enforcement, 4) drop-down list and radio button fieldconformance, and 5) form-field max-length enforcement. In someembodiments, the application firewall 290 ensures cookies are notmodified. In other embodiments, the application firewall 290 protectsagainst forceful browsing by enforcing legal URLs.

In still yet other embodiments, the application firewall 290 protectsany confidential information contained in the network communication. Theapplication firewall 290 may inspect or analyze any networkcommunication in accordance with the rules or polices of the engine 236to identify any confidential information in any field of the networkpacket. In some embodiments, the application firewall 290 identifies inthe network communication one or more occurrences of a credit cardnumber, password, social security number, name, patient code, contactinformation, and age. The encoded portion of the network communicationmay comprise these occurrences or the confidential information. Based onthese occurrences, in one embodiment, the application firewall 290 maytake a policy action on the network communication, such as preventtransmission of the network communication. In another embodiment, theapplication firewall 290 may rewrite, remove or otherwise mask suchidentified occurrence or confidential information.

C. Client Agent

Referring now to FIG. 3, an embodiment of the client agent 120 isdepicted. The client 102 includes a client agent 120 for establishingand exchanging communications with the appliance 200 and/or server 106via a network 104. In brief overview, the client 102 operates oncomputing device 100 having an operating system with a kernel mode 302and a user mode 303, and a network stack 310 with one or more layers 310a-310 b. The client 102 may have installed and/or execute one or moreapplications. In some embodiments, one or more applications maycommunicate via the network stack 310 to a network 104. One of theapplications, such as a web browser, may also include a first program322. For example, the first program 322 may be used in some embodimentsto install and/or execute the client agent 120, or any portion thereof.The client agent 120 includes an interception mechanism, or interceptor350, for intercepting network communications from the network stack 310from the one or more applications.

The network stack 310 of the client 102 may comprise any type and formof software, or hardware, or any combinations thereof, for providingconnectivity to and communications with a network. In one embodiment,the network stack 310 comprises a software implementation for a networkprotocol suite. The network stack 310 may comprise one or more networklayers, such as any networks layers of the Open Systems Interconnection(OSI) communications model as those skilled in the art recognize andappreciate. As such, the network stack 310 may comprise any type andform of protocols for any of the following layers of the OSI model: 1)physical link layer, 2) data link layer, 3) network layer, 4) transportlayer, 5) session layer, 6) presentation layer, and 7) applicationlayer. In one embodiment, the network stack 310 may comprise a transportcontrol protocol (TCP) over the network layer protocol of the internetprotocol (IP), generally referred to as TCP/IP. In some embodiments, theTCP/IP protocol may be carried over the Ethernet protocol, which maycomprise any of the family of IEEE wide-area-network (WAN) orlocal-area-network (LAN) protocols, such as those protocols covered bythe IEEE 802.3. In some embodiments, the network stack 310 comprises anytype and form of a wireless protocol, such as IEEE 802.11 and/or mobileinternet protocol.

In view of a TCP/IP based network, any TCP/IP based protocol may beused, including Messaging Application Programming Interface (MAPI)(email), File Transfer Protocol (FTP), HyperText Transfer Protocol(HTTP), Common Internet File System (CIFS) protocol (file transfer),Independent Computing Architecture (ICA) protocol, Remote DesktopProtocol (RDP), Wireless Application Protocol (WAP), Mobile IP protocol,and Voice Over IP (VoIP) protocol. In another embodiment, the networkstack 310 comprises any type and form of transport control protocol,such as a modified transport control protocol, for example a TransactionTCP (T/TCP), TCP with selection acknowledgements (TCP-SACK), TCP withlarge windows (TCP-LW), a congestion prediction protocol such as theTCP-Vegas protocol, and a TCP spoofing protocol. In other embodiments,any type and form of user datagram protocol (UDP), such as UDP over IP,may be used by the network stack 310, such as for voice communicationsor real-time data communications.

Furthermore, the network stack 310 may include one or more networkdrivers supporting the one or more layers, such as a TCP driver or anetwork layer driver. The network drivers may be included as part of theoperating system of the computing device 100 or as part of any networkinterface cards or other network access components of the computingdevice 100. In some embodiments, any of the network drivers of thenetwork stack 310 may be customized, modified or adapted to provide acustom or modified portion of the network stack 310 in support of any ofthe techniques described herein. In other embodiments, the accelerationprogram 120 is designed and constructed to operate with or work inconjunction with the network stack 310 installed or otherwise providedby the operating system of the client 102.

The network stack 310 comprises any type and form of interfaces forreceiving, obtaining, providing or otherwise accessing any informationand data related to network communications of the client 102. In oneembodiment, an interface to the network stack 310 comprises anapplication programming interface (API). The interface may also compriseany function call, hooking or filtering mechanism, event or call backmechanism, or any type of interfacing technique. The network stack 310via the interface may receive or provide any type and form of datastructure, such as an object, related to functionality or operation ofthe network stack 310. For example, the data structure may compriseinformation and data related to a network packet or one or more networkpackets. In some embodiments, the data structure comprises a portion ofthe network packet processed at a protocol layer of the network stack310, such as a network packet of the transport layer. In someembodiments, the data structure 325 comprises a kernel-level datastructure, while in other embodiments, the data structure 325 comprisesa user-mode data structure. A kernel-level data structure may comprise adata structure obtained or related to a portion of the network stack 310operating in kernel-mode 302, or a network driver or other softwarerunning in kernel-mode 302, or any data structure obtained or receivedby a service, process, task, thread or other executable instructionsrunning or operating in kernel-mode of the operating system.

Additionally, some portions of the network stack 310 may execute oroperate in kernel-mode 302, for example, the data link or network layer,while other portions execute or operate in user-mode 303, such as anapplication layer of the network stack 310. For example, a first portion310 a of the network stack may provide user-mode access to the networkstack 310 to an application while a second portion 310 a of the networkstack 310 provides access to a network. In some embodiments, a firstportion 310 a of the network stack may comprise one or more upper layersof the network stack 310, such as any of layers 5-7. In otherembodiments, a second portion 310 b of the network stack 310 comprisesone or more lower layers, such as any of layers 1-4. Each of the firstportion 310 a and second portion 310 b of the network stack 310 maycomprise any portion of the network stack 310, at any one or morenetwork layers, in user-mode 203, kernel-mode, 202, or combinationsthereof, or at any portion of a network layer or interface point to anetwork layer or any portion of or interface point to the user-mode 203and kernel-mode 203.

The interceptor 350 may comprise software, hardware, or any combinationof software and hardware. In one embodiment, the interceptor 350intercept a network communication at any point in the network stack 310,and redirects or transmits the network communication to a destinationdesired, managed or controlled by the interceptor 350 or client agent120. For example, the interceptor 350 may intercept a networkcommunication of a network stack 310 of a first network and transmit thenetwork communication to the appliance 200 for transmission on a secondnetwork 104. In some embodiments, the interceptor 350 comprises any typeinterceptor 350 comprises a driver, such as a network driver constructedand designed to interface and work with the network stack 310. In someembodiments, the client agent 120 and/or interceptor 350 operates at oneor more layers of the network stack 310, such as at the transport layer.In one embodiment, the interceptor 350 comprises a filter driver,hooking mechanism, or any form and type of suitable network driverinterface that interfaces to the transport layer of the network stack,such as via the transport driver interface (TDI). In some embodiments,the interceptor 350 interfaces to a first protocol layer, such as thetransport layer and another protocol layer, such as any layer above thetransport protocol layer, for example, an application protocol layer. Inone embodiment, the interceptor 350 may comprise a driver complying withthe Network Driver Interface Specification (NDIS), or a NDIS driver. Inanother embodiment, the interceptor 350 may comprise a mini-filter or amini-port driver. In one embodiment, the interceptor 350, or portionthereof, operates in kernel-mode 202. In another embodiment, theinterceptor 350, or portion thereof, operates in user-mode 203. In someembodiments, a portion of the interceptor 350 operates in kernel-mode202 while another portion of the interceptor 350 operates in user-mode203. In other embodiments, the client agent 120 operates in user-mode203 but interfaces via the interceptor 350 to a kernel-mode driver,process, service, task or portion of the operating system, such as toobtain a kernel-level data structure 225. In further embodiments, theinterceptor 350 is a user-mode application or program, such asapplication.

In one embodiment, the interceptor 350 intercepts any transport layerconnection requests. In these embodiments, the interceptor 350 executetransport layer application programming interface (API) calls to set thedestination information, such as destination IP address and/or port to adesired location for the location. In this manner, the interceptor 350intercepts and redirects the transport layer connection to a IP addressand port controlled or managed by the interceptor 350 or client agent120. In one embodiment, the interceptor 350 sets the destinationinformation for the connection to a local IP address and port of theclient 102 on which the client agent 120 is listening. For example, theclient agent 120 may comprise a proxy service listening on a local IPaddress and port for redirected transport layer communications. In someembodiments, the client agent 120 then communicates the redirectedtransport layer communication to the appliance 200.

In some embodiments, the interceptor 350 intercepts a Domain NameService (DNS) request. In one embodiment, the client agent 120 and/orinterceptor 350 resolves the DNS request. In another embodiment, theinterceptor transmits the intercepted DNS request to the appliance 200for DNS resolution. In one embodiment, the appliance 200 resolves theDNS request and communicates the DNS response to the client agent 120.In some embodiments, the appliance 200 resolves the DNS request viaanother appliance 200′ or a DNS server 106.

In yet another embodiment, the client agent 120 may comprise two agents120 and 120′. In one embodiment, a first agent 120 may comprise aninterceptor 350 operating at the network layer of the network stack 310.In some embodiments, the first agent 120 intercepts network layerrequests such as Internet Control Message Protocol (ICMP) requests(e.g., ping and traceroute). In other embodiments, the second agent 120′may operate at the transport layer and intercept transport layercommunications. In some embodiments, the first agent 120 interceptscommunications at one layer of the network stack 210 and interfaces withor communicates the intercepted communication to the second agent 120′.

The client agent 120 and/or interceptor 350 may operate at or interfacewith a protocol layer in a manner transparent to any other protocollayer of the network stack 310. For example, in one embodiment, theinterceptor 350 operates or interfaces with the transport layer of thenetwork stack 310 transparently to any protocol layer below thetransport layer, such as the network layer, and any protocol layer abovethe transport layer, such as the session, presentation or applicationlayer protocols. This allows the other protocol layers of the networkstack 310 to operate as desired and without modification for using theinterceptor 350. As such, the client agent 120 and/or interceptor 350can interface with the transport layer to secure, optimize, accelerate,route or load-balance any communications provided via any protocolcarried by the transport layer, such as any application layer protocolover TCP/IP.

Furthermore, the client agent 120 and/or interceptor may operate at orinterface with the network stack 310 in a manner transparent to anyapplication, a user of the client 102, and any other computing device,such as a server, in communications with the client 102. The clientagent 120 and/or interceptor 350 may be installed and/or executed on theclient 102 in a manner without modification of an application. In someembodiments, the user of the client 102 or a computing device incommunications with the client 102 are not aware of the existence,execution or operation of the client agent 120 and/or interceptor 350.As such, in some embodiments, the client agent 120 and/or interceptor350 is installed, executed, and/or operated transparently to anapplication, user of the client 102, another computing device, such as aserver, or any of the protocol layers above and/or below the protocollayer interfaced to by the interceptor 350.

The client agent 120 includes an acceleration program 302, a streamingclient 306, and/or a collection agent 304. In one embodiment, the clientagent 120 comprises an Independent Computing Architecture (ICA) client,or any portion thereof, developed by Citrix Systems, Inc. of FortLauderdale, Fla., and is also referred to as an ICA client. In someembodiments, the client 102 comprises an application streaming client306 for streaming an application from a server 106 to a client 102. Insome embodiments, the client agent 120 comprises an acceleration program302 for accelerating communications between client 102 and server 106.In another embodiment, the client agent 120 includes a collection agent304 for performing end-point detection/scanning and collecting end-pointinformation for the appliance 200 and/or server 106.

In some embodiments, the acceleration program 302 comprises aclient-side acceleration program for performing one or more accelerationtechniques to accelerate, enhance or otherwise improve a client'scommunications with and/or access to a server 106, such as accessing anapplication provided by a server 106. The logic, functions, and/oroperations of the executable instructions of the acceleration program302 may perform one or more of the following acceleration techniques: 1)multi-protocol compression, 2) transport control protocol pooling, 3)transport control protocol multiplexing, 4) transport control protocolbuffering, and 5) caching via a cache manager. Additionally, theacceleration program 302 may perform encryption and/or decryption of anycommunications received and/or transmitted by the client 102. In someembodiments, the acceleration program 302 performs one or more of theacceleration techniques in an integrated manner or fashion.Additionally, the acceleration program 302 can perform compression onany of the protocols, or multiple-protocols, carried as a payload of anetwork packet of the transport layer protocol.

The streaming client 306 comprises an application, program, process,service, task or executable instructions for receiving and executing astreamed application from a server 106. A server 106 may stream one ormore application data files to the streaming client 306 for playing,executing or otherwise causing to be executed the application on theclient 102. In some embodiments, the server 106 transmits a set ofcompressed or packaged application data files to the streaming client306. In some embodiments, the plurality of application files arecompressed and stored on a file server within an archive file such as aCAB, ZIP, SIT, TAR, JAR or other archive. In one embodiment, the server106 decompresses, unpackages or unarchives the application files andtransmits the files to the client 102. In another embodiment, the client102 decompresses, unpackages or unarchives the application files. Thestreaming client 306 dynamically installs the application, or portionthereof, and executes the application. In one embodiment, the streamingclient 306 may be an executable program. In some embodiments, thestreaming client 306 may be able to launch another executable program.

The collection agent 304 comprises an application, program, process,service, task or executable instructions for identifying, obtainingand/or collecting information about the client 102. In some embodiments,the appliance 200 transmits the collection agent 304 to the client 102or client agent 120. The collection agent 304 may be configuredaccording to one or more policies of the policy engine 236 of theappliance. In other embodiments, the collection agent 304 transmitscollected information on the client 102 to the appliance 200. In oneembodiment, the policy engine 236 of the appliance 200 uses thecollected information to determine and provide access, authenticationand authorization control of the client's connection to a network 104.

In one embodiment, the collection agent 304 comprises an end-pointdetection and scanning mechanism, which identifies and determines one ormore attributes or characteristics of the client. For example, thecollection agent 304 may identify and determine any one or more of thefollowing client-side attributes: 1) the operating system an/or aversion of an operating system, 2) a service pack of the operatingsystem, 3) a running service, 4) a running process, and 5) a file. Thecollection agent 304 may also identify and determine the presence orversions of any one or more of the following on the client: 1) antivirussoftware, 2) personal firewall software, 3) anti-spam software, and 4)internet security software. The policy engine 236 may have one or morepolicies based on any one or more of the attributes or characteristicsof the client or client-side attributes.

In some embodiments and still referring to FIG. 3, a first program 322may be used to install and/or execute the client agent 120, or portionthereof, such as the interceptor 350, automatically, silently,transparently, or otherwise. In one embodiment, the first program 322comprises a plugin component, such an ActiveX control or Java control orscript that is loaded into and executed by an application. For example,the first program comprises an ActiveX control loaded and run by a webbrowser application, such as in the memory space or context of theapplication. In another embodiment, the first program 322 comprises aset of executable instructions loaded into and run by the application,such as a browser. In one embodiment, the first program 322 comprises adesigned and constructed program to install the client agent 120. Insome embodiments, the first program 322 obtains, downloads, or receivesthe client agent 120 via the network from another computing device. Inanother embodiment, the first program 322 is an installer program or aplug and play manager for installing programs, such as network drivers,on the operating system of the client 102.

D. Server Initiated Connections to a SSL VPN Client

Referring now to FIG. 4A, an embodiment of an appliance 200 and clientagent 120 is depicted for providing a server initiated transport layerconnection between a server 106 and a client 102 connected by a virtualprivate network connection via the appliance 200. In brief overview, aclient 102 on a first network 104 may establish a virtual privatenetwork connection, such as a SSL VPN connection, via the appliance 200to a second network 104′. The appliance 200 assigns an Intranet InternetProtocol (IIP) address 282 to the client 102 or the user of the client102. A server 106 initiates a transport layer connection with the client102 using the IIP address 282. The appliance 200 intercepts thetransport layer connection request and establishes a first transportlayer connection with the server 106. The appliance 200 transmitsinformation about the connection request to the client agent 120 of theclient 102 via control connection or communication channel. With thisinformation, the client agent 120 establishes a second and localtransport layer connection with the application on the client 102. Theclient agent 120 also establishes a third transport layer connection,such as a SSL VPN connection, to the appliance 200, and associates thesecond and third transport layer connections. The appliance 200associates the third transport layer connection with the first transportlayer connection, and forwards any data from the server 106 to theclient agent 120 to forward to the application. The client agent 120receives the data via the third transport layer connection and forwardsthe data o the application via the second transport layer connection.The various details of the embodiment depicted in FIG. 4A will bedescribed later in conjunction with FIG. 4B below.

A server 106 may initiate a transport layer connection to a client 102using any kind of transport layer protocol. In one embodiment, theserver 106 may initiate a TCP connection with the client 102. In anotherembodiment, the server 106 may initiate a UDP connection with the client102. In some embodiments, the server 106 may reside on the private orintranet network 104′ accessed via the appliance 200. In otherembodiments, the server 106 may reside on an extranet, or network 104external to the appliance 200 and/or client 102.

A server 106 may initiate a transport layer connection to a client 102in different ways. The server 106 may initiate a 1) pure serverinitiated connection, 2) a client triggered initiated connection, or 3)a server initiated connection derived from information embedded in thepayload, referred to as a hybrid connection. In one embodiment, a pureserver initiated connection is when a server 106 has prior knowledgeabout the IIP address 282 and port of the SSL VPN client 102 and makes aconnection to the client 102. This connection request is intercepted bythe appliance 200. For example, a server 106 may access telnet orweb-services running on a SSL VPN logged in client 102. In someembodiments, the SSL VPN client 102 triggers the server 106 to initiatethe transport layer connection. For example, the SSL VPN client 102makes an initial connection to the server 106 and the server 106connects to the client 102 on a port that is well-known or is derivedfrom the first port used by the client 102 to connect to the server 106.

In other embodiments, the server initiated connection is a hybrid. Forexample, the client 102 makes an initial connection to the server 106and the client 102 and server 106 exchange ports and IP addresses withan application specific protocol. As such, in one embodiment, the IPaddress and port information is embedded or included in the payload ofthe transport layer packets. A NetMeeting data connection is an exampleof a hybrid server initiated connection as well as the port command usedin an active file transfer protocol (FTP) session. In these embodiments,the appliance modifies the payload exchanged between the client 102 andserver 106 to use the IIP address 282 of the client 102 or user of theclient 102.

In some embodiments, the client agent 120 and appliance communicate viaa control channel or control connection. The control channel maycomprise a UDP or TCP transport layer connection. In one embodiment, theclient agent 120 and appliance 200 establish a persistent connection forexchanging control messages. In some embodiments, this controlconnection is created by the client agent sending an HTTP GET request,or a /cs HTTP GET request to the appliance 200. In one embodiment, theappliance 200 handles SSL VPN connection requests via an HTTP handler.In another embodiment, the client agent 120 and appliance 200 can usethis control connection to send periodic “heart-beat” or health checkmessages, such as when there is not network traffic.

In some embodiments, the appliance 200 and client agent 200 may exchangecontrol messages via a control channel protocol. In one embodiment, theappliance 200 transmits control messages to the client agent 120 via amultiplex UDP channel using a UDP multiplexed header 426. In oneembodiment, the appliance 200 transmits a udp multiplexed header 426 toinform the client agent 120 of a server initiated TCP or UDP request. Byway of example only and in no way limiting the control channel protocol,the following udp multiplex header 426 is used:

typedef struct ns_udp_mul_head {   u08bitsver; // version   u08bitstyppro; // 0xF0: Type, 0x0F: protocol   u16bits len; // Length of data  u32bits sip; // Network Order Server IP   u32bits cip; // NetworkOrder Client IP   u16bits sport; // Network Order Server Port   u16bitscport; // Network Order Client Port   u16bits ipid; // IP ID when needed  u16bits padding; // Must be zero } ns_udp_mul_head_t;Although a control message protocol from the appliance 200 to the clientagent 120 is generally described above with data elements of a certaintype and size and for holding a certain value, the control messageprotocol may use any type and form of header or data structure of a widevariety of types and sizes to convey server initiated connectioninformation and values to the client agent 120 in performing theoperations described herein.

In one embodiment, the client agent 120 opens a connection to theapplication on the tuple <localhost, destport, typeproto>. The clientagent 120 opens a new connection to the appliance 200 and links it tothe application connection. In case of TCP, the 3-tuple sent by theappliance 200 is sent back as part of the new connection from the clientagent 120. This allows the appliance 200 to find out which serverinitiated connection this belongs to. In response to a TCP serverinitiated connection request from the appliance 200, the client agent120 opens a connection to the appliance 200, in one embodiment, byissuing a /controlack HTTP POST request. By way of example, the clientagent 12-issues the following request:

POST /controlack HTTP/1.1\r\n PROTOCOL: TCP\r\n COOKIE:session=loginid\r\n Content-Length:8\r\n \r\n <BODY will includeCLNTPORT :< destport received in control message> CSPORT: <srcportreceived in control message>, CSIP: <srcip received in control message>,>

If the client agent 120 cannot open a connection to the application onlocalhost, the client agent 120 may indicate an error by re-sending theudp-multiplexed header 426 with len set to 0. In some embodiments, thisheader 426 includes the 3-tuple the client agent 120 received previouslyso that the appliance 200 can clean up the server side connection. Incase of TCP, the appliance 200 may send a reset. In case of UDP, theappliance may send a port unreachable Internet Control Message Protocol(ICMP) error.

In some embodiments, the appliance 200, such as in the kernel, managesor handle UDP data via a client and server network address translation(nat) protocol control block (pcb) pair, or natpcb pair. In oneembodiment, a process control blocks or pcbs 422, 422 may be used tostore, track and maintain information regarding a socket or socketconnection. For example, a PCB may store information and track a stateof a socket connection. In some embodiments, a PCB comprises a record ofinformation on a state or attributes of a connection, such as aconnection record. A natpcb may store information and track a state orthe network address translation of a socket connection traversingbetween a first network and a second network. The appliance 200 creates,tracks, updates and maintains, in a table, database, memory or otherstorage, client and server side PCBs 422, 424 and natpcbs in providingthe operations described herein.

Although the state, information and connection management of varioustransport layer connections are generally described herein using aprocess control block (pcb), any type and form of connection record maybe used to store, hold, maintain and track any information related to aconnection, or socket thereof. A connection record may comprise anyinformation stored in a data structure or object in memory. A connectionrecord may comprise any storage element, such as a table, database orentries in a table or database. The appliance 200 may manage, organizeand track one or more connection records in memory (data structure orobject), or in storage (table or database).

For server-initiated connections, in one embodiment, the appliancecreates the server natpcb 422 with the connection parameters transmittedfrom the server 106. The appliance 200 creates the client natpcb 422with the tuple <localhost, destport, mip, mport>, and this may also beused in the multiplex header 426 as shown by way of example via thetable below. The mip and mport are for Mapped IP embodiments, where theappliance maps the client IP address and port to an appliance providedIP address and port.

Client 102 Server 106 GET /cs HTTP/1.1 200 OK . . . . . .ns_udp_mul_head_t packet over control channel POST /controlack HTTP/1.1PRTCL: TCP COOKIE: session=loginid Content-Length:8 <2 bytes forCLNTPORT> <2 bytes for CSPORT> <4 bytes for CSIP> HTTP/1.1 200 OK

In one embodiment, the appliance 200 establishes a listener process 460upon establishment of the connection 440 and/or upon login of the user.In some embodiments, the listener process comprises an application,program, service, thread, task or other set of executable instructionsto listen for transport layer connection messages. In some embodiments,the listener 260 is a TCP or UDP socket based listener. In oneembodiment, the appliance 200 hosts the IIP address 282 of the user orthe client 102. In these embodiments, the appliance 200 provides thelistener process 460 to act as, spoof or otherwise virtualize the client102 as available on the network 104′. As such, in some embodiments, theappliance 200 via the listener 260 listens for any networkcommunications transmitted to the IIP address 282 of the client 102. Inone embodiment, the listener 460 registers itself and/or the IIP addresswith registration service or database 420. In one embodiment, theregistration service 420 comprises a pcb, information about a pcb orassociation of pcbs. In other embodiments, the registration service 420includes information about the server 106, such as any IP and portinformation of the server's connection with the application. In someembodiments, the registration service 420 associates the server 106 withthe client's IIP address 282 it has initiated a connection to.

Referring now to FIG. 4B, details of steps of an embodiment of a methodfor practicing server initiation connections with the appliance 200 andclient agent 120 is depicted. FIG. 4B will be described and discussed inconjunction with FIG. 4A as the steps of method 450 are referenced inthe diagram of FIG. 4A. In brief overview, at step 400, the server 106initiated a transport layer connection to the client 102. At steps 401,402 and 403, the appliance 200 and server 106 perform a transport layerconnect handshake to establish a first transport layer connection. Atstep 404, the appliance 200 generates a protocol control block (pcb) 422representing the appliance 200 to server 106 connection, e.g., the firsttransport layer connection. At step 405, the appliance 200 transmits acontrol packet to the client agent 120 via the control connection. Thecontrol packet may use the mux header 256 to identify the connectiontuple. At step 406, the client agent 120 initiates a local connection,e.g., a second transport layer connection, with the application on theclient 102 using the tuple from the control packet. At step 407, theclient agent 120, via interceptor 350, intercepts packet sent to theserver IP address and port. At step 408, the client agent 120establishes a new transport layer connection, e.g., a third connectionor SSL VPN connection, with the appliance 200. At step 409, theappliance 200 generates a client-side HTTP protocol control block 424.At step 410, the client transmits a control ack message via theestablished third connection. At step 411, the appliance 200 retrievesthe client-side TCP SYNC protocol control block 422 and associates itthe client-side HTTP protocol control block 424. At step 412, theappliance 200 forwards data received from the server, e.g., from serverIP and server source port, via the first transport layer connection tothe client agent 120 via the third transport layer connection and theclient agent 120 provides the data to the application via the secondtransport layer connection.

In further details, at step 400, the server 106 initiates a transportlayer connection to the client 102 via any one of a number of differentways and may use any type and form of transport layer protocol. In oneembodiment, the server 106 initiates a TCP connection to the client 102.In another embodiment, the server 106 initiates a UDP connection to theclient 102. In one embodiment, the server 106 makes a pure serverinitiated connection. In another embodiment, the server 106 makes aclient triggered server initiated connection. In some embodiments, theserver 106 makes a hybrid server initiated connection by which theclient 102 and server 106 exchange connection information via anapplication layer protocol and payload. In one embodiment, the server106 resides on the intranet of the appliance 200. In other embodiments,the server 106 may be external to the appliance 200, client 102 andnetworks 104 or 104′.

In some embodiments, the appliance 200 determines the number of serverinitiated connection requests to the client 102 exceeds a predeterminedthreshold or quantity. For example, the appliance 200 may be configuredto only establish a maximum number of server initiated connections toany one client. This predetermined maximum may be configurable by auser, such as an administrator. In another example, the appliance 200may be configured to only establish a maximum number of server initiatedconnections to any of the VPN connected clients. Upon determining theserver initiated connection request exceeds the predetermined threshold,the appliance 200 does not establish the server requested connection. Inone embodiment, the appliance 200 drops the request. In anotherembodiment, the appliance 200 denies the request. In yet anotherembodiment, the appliance 200 responds with an error to the server 106.In some embodiments, the appliance 200 responds to the server 106 withan indication the number of server initiated connections allowed hasbeen exceeded. In yet other embodiments, the appliance 200 does notperform any of the remaining steps of method 450.

At steps 401, 402, and 403, the server 106 and appliance 200 perform atransport layer connection handshake. In one embodiment, the transportlayer handshake comprises a TCP handshake. For example, at step 401, theserver 106 transmits a TCP SYN packet. In response, at step 402, theappliance 200 transmits a TCP SYN-ACK packet 402. In response to the TCPSYN-ACK and to complete the handshake, the server 106 transmits a TCPACK packet. In other embodiments, the method 450 is practiced withoutthe handshake of steps 401, 402 and 403, such as in the case of UDP,which is a connectionless protocol. In other embodiments, a secure UDPconnection may be used, in which a handshake of any of the steps of 401,402 or 403 are performed, such as for an SSL or TLS UDP connection.

At step 404, the appliance generates, creates or otherwise provides aprotocol control block (pcb) for the appliance to server connection. Inone embodiment, the appliance 200 creates a client side pcb 422 uponsuccessful establishment of the first transport layer connection betweenthe appliance 200 and the server 102. In some embodiments, the pcb 422is referred to as a client side TCP SYNC pcb as it represents thesuccessful establishment of the handshake of steps 401 through 403. Inthese embodiments, the pcb 422 represents the state of the socket orsocket connection of the first transport layer connection. From theperspective of the server 106, in one embodiment, it appears to theserver 106 that it has established the transport layer connection withthe client 102.

At step 405, the appliance 200 transmits a control message to the clientagent 120 via a control connection or communication channel 430. In someembodiments, the control channel 430 comprises a UDP multiplexedchannel. In other embodiments, the control channel 430 may comprise anytype and form of connection, including a TCP connection, SSL VPNconnection 440, or any other transport layer connection. In oneembodiment, the appliance 200 and client agent 120 communicate via anHTTP connection. In some embodiments, the appliance 200 determines theclient agent 120 to transmit the control message by the IIP address 282of the client 102 used in the server initiated transport layerconnection request. In one embodiment, the IIP address 282 is assignedby the appliance 200 to the user of the client 102. In anotherembodiment, the IIP address 282 is assigned to the client 102. Theappliance 200 may track the IIP address 282 via a table, databasemapping IIP addresses to clients 102 or users. In one embodiment, theappliance 200 may have a natpcb providing the IIP address mapping.

In one embodiment, the appliance 200 sends a message to the client agent120 identifying information related to the server imitated connectionrequest, including any of the protocol, the port number of the client,the IP address of the server 106, and the port of the server 106. Insome embodiments, the appliance 200 transmits to the client 102 theclient's IIP address 282. The appliance 200 may determine the relevantsession and corresponding tuple information based on the IIP address282. In some embodiments, the appliance 200 transmits a UDP multiplexedheader 426 to the client agent 120 that comprises informationidentifying the following information: <server IP, server port, ClientIP, client port>. In the case of a server initiated UDP transport layerconnection request, the appliance 200 pre-pends the UDP multiplexedheader 426 to a UDP datagram and transmits the UDP datagram to theclient agent 120.

At step 406, the client agent 120 establishes a second transport layerconnection with an application on the client 102. For example, theapplication may be the intended recipient or target of the serverinitiated connection request, such as NetMeeting, active FTP, a telnetsession or web service. In one embodiment, the client agent 120determines the type of protocol, for example, whether the serverinitiated connection request is TCP or UDP, from the header 486. In thecase of TCP type protocol, the client agent 120 creates a newclient-side protocol control block. In some embodiments, the clientagent 120 initiates a local transport layer connection to theapplication using <server IP, server port, Client IP, client port>. Inone embodiment, the client agent 120 makes a local loopback connectionusing the client port number identified by the control message and localIP address of the client 102.

At step 407, the client agent 120 intercepts one or more network packetstransmitted by the application to the destination of <server IP (SIP),server port>. In some embodiments, the interception mechanism 350 of theclient agent 120 intercepts the network packets. In one embodiment, theinterception mechanism 350 comprises a Transport Driver Interface (TDI)layer interception mechanism to intercept transport layer networkpackets. In another embodiment, the client agent 120 or interceptionmechanism 350 intercepts network packets of the application seamlesslyand/or transparently to the application or user of the application. Insome embodiments, the client agent 120 intercepts the network packetstransmitted via the second transport layer connection or localconnection in order to transmit the network packets via third transportlayer connection to the appliance 200. In one embodiment, the clientagent 120 spoofs the local connection 450 to have a source IP address ofthe server 106.

At step 408, the client agent 120 establishes a transport layerconnection, or third connection, 440 with the appliance 200. In someembodiments, the client agent 120 establishes a SSL VPN connection 440.In one embodiment, the client agent 120 and appliance 200 perform a SSLor TLS handshake to establish a secure session over the transport layerconnection. In one embodiment, the client 102 establishes a transportlayer connection with a vServer 275 of the appliance 200. As such, insome embodiments, the client agent 120 connects to the IP address andport number of the vServer 275. In other embodiments, the client agent120 established a connection to the appliance 200 using the IP addressof the client 102 on the first network 104 as the source IP address. Inanother embodiment, the client agent 120 uses a source port available onthe client 102 to establish the transport layer connection with theappliance 200. In one embodiment, the client agent 120 associates thesecond transport layer connection, or local connection 450, with thethird transport layer connection 440 to the appliance 200.

At step 409, the appliance 200 provided or obtains a protocol controlblock (pcb) 424 for the third transport layer connection 440 between theclient agent 120 and appliance 200. In some embodiments, this pcb 424 isreferred to as the client-side HTTP pcb 424 for the SSL over TCPconnection 440. In one embodiment, the appliance generates the pcb 424.In other embodiments, the appliance 200 receives the pcb 424 from theclient agent 120. In yet another embodiment, the pcb 424 comprises a pcbfrom a previous client-side SSL TCP connection of the client 102.

At step 410, the client agent 120 transmits a message to the appliance200 via one of the control connection 430 or the newly established SSLTCP connection 440. In one embodiment, the client agent 120 transmits acontrol message providing the tuple information of client port, serverIP address and server port that was provided in the control connectmessage of step 405. In another embodiment, the control ack messageincludes the following: <server IP, server port, Client IP,client-port>. In further embodiments, the control ack message may alsoidentify the type of protocol. In some embodiments, the client agent 120transmits a control acknowledgement process control block (pcb),referred to as ctrl_ack_pcb or control_ack_pcb, via the SSL TCPconnection 440. The appliance 200 may respond to the control message ofthe client agent 120. For example, in one embodiment, the appliance 200responds with a 200 OK response for the /controlack pcb.

At step 411, the appliance 200 associates the client-side TCP SYNC pcb422 with the client-side HTTP pcb 424. In one embodiment, the appliance200 retrieves or lookups up the TCP SYNC pcb 422 associated with theclient 102 or IIP address 282 of the client or user of the client. Insome embodiments, the appliance 200 maintains the association of thepcbs 422, 424 in a table, database, or other storage location. Inanother embodiment, the appliance 200 provides for the association ofthe pcbs 422, 424 in a data structure or object in memory. In yetanother embodiment, the appliance 200 uses a pcb to track theassociation between the pcbs 422 and 424.

At step 412, upon establishment of the third transport layer connection440, and the association of pcbs, the appliance forwards data from theserver 106 received via the first transport layer connection to theclient agent 120 via the third transport layer connection 440. In oneembodiment, data from or associated with the client ctrlack_pcb 424 isintercepted by an appliance client handler and forwarded to the sinc_pcb422. In some embodiments, the data associated or from sinc_pcb 422 ishandled by the appliance 200 via a server-side or tcp handler andforwarded or sent on the ctrlack_pcb 424. In one embodiment, theappliance 200 establishes a listener process 460 upon establishment ofthe connection 440 and/or upon login of the user. In some embodiments,the listener process 460 listens for incoming data from the server 106to forward to the client agent 120 or client 102. In one embodiment, theappliance 200 forwards data coming from the server's IP address andserver source port to the client IP address and port number of theclient agent 120 of the third transport layer connection 440. In anotherembodiment, the client agent 120 intercepts traffic from the applicationdirected towards the IP address and port of the server, and forward thetraffic to the appliance 200 to forward via the first transport layerconnection.

In view of the steps of method 450 described above, in some embodimentsof a hybrid type of server initiated connection, the appliance 200 mayintercept and modify any of the network packets transmitted between theclient 102 and server 106. As the connection information may be embeddedin the payload of these network packets, the appliance 200 may read suchinformation from the payload in practicing any of the steps of method450 described above. Additionally, the appliance 200 may modify any ofthe network packets between the client agent 120 and the appliance 200in order for the server initiated connection to operate at anapplication layer protocol level in accordance with the operationsdescribed herein. For example, the appliance 200 may modify any networkpacket to change the client IP address to the IIP address 282. In otherexamples, the appliance 200 may modify any network packets to map theconnection information from the server to the third transport layerconnection client agent 120, and vice-versa (from the client agent tothe server).

In the case of errors in establishing or user of the server initiatedconnection, the appliance 200 and client agent 120 may communicate suchevents in order to clean up any of the plurality of connections and tofree up resources. For example, in one embodiment, if the client agent120 fails to connect to the application after receiving the ServerInitiated Connection request, the client agent 120 sends an error packetor error control message to the appliance. The appliance 200 then closesthe server side transport layer connection. In another embodiment, ifthe appliance to server connection is not alive when the client agent120 posts its controls acknowledgement to the appliance 200, theappliance 200 sends an HTTP error response to the client agent 120,which then closes the second loop back TCP connection to the appliance,and the third transport layer connection to the appliance 200. Theclient agent 120 then in one embodiment cleans up the associatedresources.

In some embodiments, if the client agent 120 cannot send data to theapplication, the client agent 120 closes the connection to theapplication and the connection to the appliance. In other embodiments,the client agent 120 logs any errors sending and receiving data, such asin the case of a UDP server initiated connection. In one embodiment,upon getting an error indication from the client agent 120, theappliance 200 resets the server connection if the protocol type orconnection type is TCP, and in the embodiment of UDP, the appliance 200sends a ‘Port Unreachable’ ICMP error message to the server. In yetanother embodiment, then the server 106 closes the connection or anerror occurs on the server side connection, the appliance 200 closes thecorresponding client side connection.

In view of the structure, functions and operations of the appliance andclient agent described above, systems and methods are provided for aflexible, efficient and transparent method of handling and managingserver initiated connections to SSL VPN clients connected to a networkvia the appliance. As such, servers and SSL VPN clients cantransparently communicate via connections established by either theserver or the client. Although generally described above as a serverinitiated connection, any computing device, such as another client,connected to the network of the appliance may initiate a connection toan SSL VPN client. The SSL VPN clients seamlessly appear as clients onthe network accessed or managed by the appliance. This enables SSL VPNusers to take advantage of applications, such as collaboration tools,that use server initiated connections. Additionally, clients of SSL VPNusers can provide access to applications and collaboration tools to theother clients and servers on the intranet of the appliance.

Many alterations and modifications may be made by those having ordinaryskill in the art without departing from the spirit and scope of theinvention. Therefore, it must be expressly understood that theillustrated embodiments have been shown only for the purposes of exampleand should not be taken as limiting the invention, which is defined bythe following claims. These claims are to be read as including what theyset forth literally and also those equivalent elements which areinsubstantially different, even though not identical in other respectsto what is shown and described in the above illustrations.

1. A method comprising: (a) receiving, by a device intermediary to aserver operating on a first network and a plurality of clients, atransport layer connection request from the server to connect to aclient, the client operating on a second network, the transport layerconnection request identifying a destination internet protocol addressof the client on the first network and a destination port on the firstnetwork; (b) establishing, by the device, a first transport layerconnection to the server on the first network; (c) determining, by thedevice, an internet protocol address of the client on the second networkcorresponding to the destination internet protocol address of the clienton the first network; (d) establishing, by the device, a secondtransport layer connection with the client at the internet protocoladdress on the second network; and (e) associating, by the device, afirst connection record for the first transport layer connection with asecond connection record for the second transport layer connectionlinked to the first transport layer connection.
 2. The method of claim1, wherein step (a) further comprises receiving, by the device, thetransport layer connection request from the server responsive toinitiating by the server to connect to the client.
 3. The method ofclaim 1, wherein step (a) further comprises receiving, by the device,the transport layer connection request from the server responsive to theclient triggering the server to initiate connection to the client. 4.The method of claim 1, wherein step (a) further comprises receiving, bythe device, the transport layer connection request from the serverresponsive to the server deriving information about the client from apayload of a transport layer packet.
 5. The method of claim 1, furthercomprising forwarding, by the device, data sent by the server via thefirst transport layer connection to the client via the second transportlayer connection.
 6. The method of claim 1, further comprisingforwarding, by the device, to the server data received by the clientthat identifies the server's internet protocol address on the secondnetwork.
 7. The method of claim 1, wherein step (a) further compriseshosting, by the device, the destination internet protocol address of theclient on the first network.
 8. The method of claim 1, wherein step (a)further comprises establishing, by the device, a listener process tolisten for network traffic from the first network on the destinationinternet protocol address of the client on the first network.
 9. Themethod of claim 1, wherein step (c) further comprises identifying theinternet protocol address of the client on the second network mapped tothe destination internet protocol address of the client hosted by thedevice on the first network.
 10. The method of claim 1, wherein step (c)further comprises identifying the port of the client on the secondnetwork mapped to a destination port of the client hosted by the deviceon the first network.
 11. A system comprising: a device, intermediary toa server operating on a first network and a plurality of clients,receiving a transport layer connection request from the server toconnect to a client, the client operating on a second network, thetransport layer connection request identifying a destination internetprotocol address of the client on the first network and a destinationport on the first network; and a virtual server of the deviceestablishing a first transport layer connection to the server on thefirst network, determining an internet protocol address of the client onthe second network corresponding to the destination internet protocoladdress of the client on the first network, and establishing a secondtransport layer connection with the client at the internet protocoladdress on the second network, wherein the device associates a firstconnection record for the first transport layer connection with a secondconnection record for the second transport layer connection linked tothe first transport layer connection.
 12. The system of claim 11,wherein the second network is not routable from the first network. 13.The system of claim 11, wherein the device receives the transport layerconnection request from the server responsive to initiating by theserver to connect to the client.
 14. The system of claim 11, wherein thedevice receives the transport layer connection request from the serverresponsive to the client triggering the server to initiate connection tothe client.
 15. The system of claim 11, wherein the device receives thetransport layer connection request from the server responsive to theserver deriving information about the client from a payload of atransport layer packet.
 16. The system of claim 11, wherein the deviceforwards data sent by the server via the first transport layerconnection to the client via the second transport layer connection andforwards to the server data received by the client that identifies theserver's internet protocol address on the second network.
 17. The systemof claim 11, wherein the device hosts the destination internet protocoladdress of the client on the first network.
 18. The system of claim 11,wherein the device establishes a listener process to listen for networktraffic from the first network on the destination internet protocoladdress of the client on the first network.
 19. The system of claim 11,wherein the virtual server identifies the internet protocol address ofthe client on the second network mapped to the destination internetprotocol address of the client hosted by the device on the firstnetwork.
 20. The system of claim 11, wherein the virtual serveridentifies the port of the client on the second network mapped to adestination port of the client hosted by the device on the firstnetwork.